1. Technical Field
The present invention relates to guard wafers, and more specifically, to guard wafers used in semiconductor structure fabrication.
2. Related Art
A typical thin film deposition process for forming a thin film on a device wafer (i.e., a wafer on which electrical devices are to be formed) is usually performed in a process chamber. More specifically, the device wafer is placed on and held in place by an electrostatic chuck in the process chamber, and then the thin film is deposited on the device wafer. Sometimes, the process chamber is conditioned by depositing a thick metal (e.g., copper) layer on all surfaces inside of the process chamber. The purpose of this thick metal layer is to absorb and restrain particles residing on the surfaces inside the process chamber so that these particles will not interfere with the ensuing thin film deposition processes performed in the process chamber. However, the thick metal layer will also form on the electrostatic chuck. As a result, a device wafer to be processed after the process chamber is conditioned, when being placed on the electrostatic chuck, could not come into direct physical contact with the top surface of the electrostatic chuck. Therefore, the device wafer could not be tightly coupled to the electrostatic chuck. This might detrimentally affect the accuracy of the ensuing fabrication steps.
As a result, there is a need for an apparatus (and method for operating the same) which allows tightly coupling the device wafer to the electrostatic chuck of the process chamber after the process chamber is conditioned.